Hydraulic positioning means for trencher boom



July 15, 1958 w. E. GEORGE ETAL 2,

HYDRAULIC POSITIONING MEANS FOR TRENCHER BOOM Filed Aug. 5, 1954 2 SheetsSheet 1 FIG. 3-

1N VEN TOR5'.

July 15, 1958 w, GEORGE ETAL 2,842,873

HYDRAULIC POSITIONING MEANS FOR TRENCHER BOOM Filed Aug. 3, 1954 2 Sheets-Sheet 2 FIG. 4. 44 3] ,QWII w HYDRAULIQ POSITIONING MEANS FOR TRENCHER BGOM Application August 3, 1954, Serial No. 447,588

4 Claims. (Cl. 37-86) The present invention relates to trenchers and more particularly to means for positioning the boom which carries the digging chain.

It is a primary object of the present invention to provide a novel hydraulic means for positioning a trenching boom which is easy and convenient to control, which is positive in operation, and which is inexpensive to construct and maintain.

It is another object to provide an hydraulic operator for a trenching boom which is capable of exerting a powerful force to swing the boom clear of the earth and into elevated or transport position and in which the boom may be hydraulically locked in any position within its range of movement.

It is a further object to provide a boom positioning and lifting device for a trencher which supplies pure torsional force to the boom housing and which applies only limited stresses to the main frame of the trencher.

It is still another object to provide an hydraulic boom operator which is conveniently constructed in a simple unit or package, which is compact and lightweight, which is capable of being powered by the pressure fluid normally available on a trenching vehicle, and which may be readily installed and conveniently removed when servicing becomes necessary.

Other objects and advantages of. the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

Figure 1 is a perspective view in partial section showing the boom lifting device installed in a light-duty trencher unit.

Figure 2 is a view similar to Figure 1 showing the boom upraised for transport.

Figure 3 is a fragmentary perspective, partially diagrammatic, showing the boom lifting device and the hydraulic control unit therefor.

Figure 4 is a longitudinal section showing the mechanism enclosed in the sub-frame.

Figure 5 shows the wedge block used for tensioning the chain.

Figure 6 shows the wedge block mounted in the subframe.

Figure 7 shows a bearing shoe for mounting the sprocket.

Figure 8 is a perspective of the boom lifting unit in partial section and as viewed from the top.

Figure 9 shows the boom lifting unit as viewed from the bottom and with the sprocket chain removed to bring out the details of construction.

While the invention has been described in connection with the preferred embodiment, it will be understood that we do not intend to be limitedto such embodiment but intend to include all modifications and alternative constructions which are included within the spirit and scope of theappended claims.

Referring now to the drawings, the present invention is shown applied to a trencher having a frame 10 mounted on the main frame F of a tractive vehicle 11 which may I nited States Patent G be a tractor or, as in the present instance, a type of vehicle commonly referred to as a jeep distinguished by sturdiness, good traction and speed. Extending from the trencher frame 10 and pivoted thereto for fore and aft rocking movement between a digging position and a transport position is a boom 12 carrying a digger chain 13 having a series of digger blades 14. Mounted on the boom 12 and coupled to the chain 13 are angers 16, 17 having oppositely directed flights for moving the earth outwardly away from the trench, the trench being indi cated at 18. Means are provided in the trencher for driving the chain as the vehicle 11 crawls slowly forward. In order to understand the construction of such driving mechanism, reference is made to Schmidt Patent 2,519,075, which issued August 15, 1950. Reference may also be made to Schmidt Patent 2,519,077 describing the construction and operation of the angers 16, 17 and to Schmidt Patent 2,519,076 which describes the construction of the digger blades 14. For present purposes, however, it will sufiice to limit attention to the drawings in the present case and particularly to Fig. 3 which shows the mounting and driving arrangement for the boom 12. The boom 12 is mounted at its inner end on a boom housing 20 which includes a pair of laterally extending hollow shafts 21, 22. For the purpose of pivoting the housing at the rear end of the tractor, bearing blocks 23, 24. are provided which are securely fastened to the rear end of the trencher frame 10. In order to drive the chain 13 a sprocket 25 is provided at the inner end of the boom 12. This sprocket is coupled to a drive sprocket 26 by a shaft (not shown) which extends through the hollow shaft 21. As discussed in the abovementioned Schmidt Patent 2,519,075, the drive sprocket 26 is driven by a chain 2'7 from the vehicle engine through a suitable step down transmission so that the speed of the digger chain is coordinated with the forward speed of the vehicle 11.

For the purpose of rocking the boom housing 20 in the bearing blocks 23, 24, an hydraulic lift unit 30 is provided constructed .in accordance with the present invention, the structure being set forth in some detail in Figs. 4-9, inclusive. The lift unit 30 includes a sub-frame 31 having opposed walls 32, 33 which extend fore and aft on the vehicle, being clamped to the main frame F (Fig. '1) by bolts or the like passing through a cross member 34. Bridging the walls at their forward ends is an end portion 35. It will be understood that the subframe is either welded together or cast in one piece to provide a box-like construction having a high degree of strength and rigidity. Journaled in the frame 31 at its rear end are a pair of sprockets 41, 42, coupled to the hollow shaft 22 which forms a part of the boom housing. Engaging the sprockets are sprocket chains 43, 44, respectively, which are arranged in a loop, the ends being pin-anchored in anchor blocks 45, 46, integrally formed on. the sprockets 41, 42. The chains are arranged side by side as shown in the drawings but are laterally spaced to define a longitudinal space between them. The sprockets 41-, 42 may be characterized as one-tooth sprockets having a cylindrical supporting surface providing maximum bearing area for supporting the sprocket chain. At the forward portion of the subframe 31 the sprocket chains 43., 44 are looped around idlers 47, 45% which are rotatably mounted on a shaft 49. The sprockets and idlers produce a straight run of chain longitudinally in the sub-frame 31.

supported relative to the shaft 49 on a pedestal 66.

two chains and lies in the plane defined by the straight run portion thereby insuring that balanced forces are applied to the chains and eliminating side thrust on the piston rod 54. It will be apparent to one skilled in the art that the travel of the plunger should correspond approximately to the length of straight run of the chains in accordance with one of the more detailed aspects of the present invention novel means are provided for tensioning or preloading the sprocket chains thereby to eliminate play between the actuator piston and the boom housing. In the present instance this is accomplished by journaling the sprockets 41, 42 at the rear end of the frame on an arcuate bearing shoe 60, the bearing shoe being slidable in longitudinal slots 61, 62 machined in the Walls of the frame. Adjustable means are further provided for pressing outwardly against the bearing shoe to vary the center-to-center distance of the sprockets and idlers. 'present instance this is accomplished by a wedge block '63 having wedges 64, 65 which are moved relatively to In the one another by means of a screw 67 engaging both of them (Fig. One side of the wedge block bears directly against the bearing shoe 60. The other side is It "will be apparent that rotating the screw 67 by means of an Allen head wrench or other suitable tool causes the bearing shoe 60 to be squeezed outwardly thereby tensioning the two chains 43, 44. Because of the high mechanical advantage provided in the wedge block, the adjustment is self-locking and once adjusted need not be touched for long periods of time.

For the purpose of controlling admission of pressure fluid to the actuator 50 a double-acting control valve 70 is provided as shown more or less diagrammatically in Fig. 3. Pressure fluid is supplied from a gear pump 68 or the like, constant pressure being obtained by an unloading type of relief valve 69. One skilled in the art will appreciate that the valve 69 may be set to release fluid whenever the pressure tends to exceed a preset value. The valve 70 includes a movable spool 71 which is moved axially by means of a manual lever 72. The spool includes lands 73, 74. Arranged for blocking by the lands when the valve is in its midposition are ports 75, 76 which are connected as shown to ports 77, 78 at the respective ends of the actuator 50. Pressure fluid is supplied to the valve 70 from the pump 68 via an inlet port 80. Pressure fluid is exhausted at the center of the valve through outlet port 81 to the fluid sump.

in order to lower the boom to the digging position the control lever 72 is moved to its down position which serves to supply pressure fluid to the rear end of the actuator via the ports 76, 78. Simultaneously, fluid is exhausted via ports 75, 77 to the sump. Plunger movement continues until the control valve 70 is manually restored to its central locked position.

When the valve is in the mid position, the fluid from the cylinder is blocked and, consequently, the piston rod is locked in the desired position, for example the position required to dig a trench of a given depth. In order to insure that the boom is maintained in such position and to avoid the effects of leakage in the valve 70, a pilot-operated check valve 90 is provided. Such check valve is inserted in the line 76 which supplies fluid under pressure to the actuator 50 for movement in the downward direction. Included in the check valve 90 is a ball 91 biased by a spring 92 against a seat 93 to prevent reverse flow of fluid from the actuator when the boom is in normal working position. Means are included in the check valve for unseating the ball 91 when it is desired to raise the boom. This is accomplished by a piston 94 connected to the line as shown in Fig. 3, such piston having a rod for engaging the ball 91. It will be apparent that when the valve is moved to the up position, pressure in the line 75 causes movement of the piston 94 to unseat the ball 91, thereby permitting reverse flow of fluid through the check valve. The operation may be readily controlled from the drivers seat or other convenient position and achieves a high degree of operating convenience.

It is one of the features of the present arrangement that the mechanical advantage between the boom housing and the hydraulic actuator remains constant over the entire range of movement. Thus, when the boom is in its downwardly hanging position, the weight component is minimized and almost the entire force of the actuator is available to overcome any interference between the blades and the walls of the trench, enabling the blades to break clear of clay, rocks or other obstruction and insuring that the boom will not get stuck in its lowered position. After the boom has swung upwardly to its horizontal position clear of the earth, all of the torque is available for overcoming the overhanging weight.

One of the additional advantages of the present arrangement is that all of the mechanical parts serving to operate the boom are protected against breakage when striking an obstruction during lowering or raising, provided only that the relief valve 69 is adjusted to limit the maximum pressure to a safe value. Thus in a typical operation the boom is lowered into contact with the ground and the driving mechanism is coupled to the digger chain. As the chain rotates the control lever 72 is advanced toward the down position thereby slowly lowering the boom into the ground. If desired the control lever may be periodically returned to the central or locked position to allow the digger blades to catch up with the downward progress of the boom. Because the torque is limited, injury because of unskilled or careless operation, for example lowering the boom too rapidly, is avoided.

In a practical design and with the relief valve set at a proper value, say, 1,500 pounds per square inch, the force on the piston rod may reach 18,000 pounds. However, because of the fact that the piston rod is centered between the chains and in the plane of the chains, the lateral and vertical forces are perfectly balanced and the net force in the piston rod is pure tension or compression, enabling use of a piston rod of limited diameter and largely avoiding sealing and wear problems at the point of entry of the piston rod into the actuator.

It is to be particularly noted that such large pressures are contained totally within the sub-frame 31 and only moderate stresses are transmitted to the main frame or to the boom housing. Thus, the force applied to the boom housing is purely torsional, permitting the bearing 24 to be made relatively small in size. The only force transmitted to the main frame is the vertical loading transmitted to the frame by the cross member 34 on the sub-frame. This consists of the weight of the sub-frame and enclosed parts plus the reaction torque from the boom, which under normal operating conditions does not exceed about 3,000 pounds, a force which is readily resisted by a pair of fastening bolts. The high forces associated with the actuator are readily absorbed in the subframe 31 which is of rigid box-like construction and which may be made as strong as desired without greatly adding to the weight.

It will be apparent that the device is of simple and durable construction and is capable of operating over long periods of time without care or maintenance, even when operated by relatively untrained personnel. Be-

cause of the unit construction the device may be removed from the vehicle for bench work when maintenance or inspection are necessary.

We claim as our invention:

1. In a hydraulic operator for a trenching boom, said boom having a rotatable boom housing journalled in a main frame, the combination comprising, a sub-frame mounted on said main frame, said sub-frame having parallel walls and an end portion, a sprocket and an idler journalled in the walls of said sub-frame and spaced from one'another in line with the end portion of said sub-frame, first and second loops of chain trained about said sprocket and said idler and laterally spaced from one another, a double-acting hydraulic actuator mounted on the end portion of said sub-frame and having a plunger centered between the loops and coupled to said chain at the straight run portion thereof defined by said sprocket and said idler, so that linear movement of said plunger in one direction or the other produces rotation of said sprocket likewise in one direction or the other, and means for rigidly coupling said sprocket coaxially to said boom housing for imparting motion of the plunger in either direction to said boom housing, for lowering the trenching boom and forcibly feeding it into the ground to the digging position, and for raising the boom to an elevated position.

2. In a hydraulic operator for a trenching boom, said boom being mounted for fore and aft rocking movement in a main frame, the combination comprising, a subframe mounted on said main frame, said sub-frame having parallel walls and an end portion, a sprocket and an idler journalled in the walls of said sub-frame and spaced from one another in line with the end portion of said sub-frame, a loop of chain trained about said sprocket and said idler, a double-acting hydraulic actuator mounted on the end portion of said sub-frame and having a plunger coupled to said chain at-the straight run portion thereof defined by said sprocket and said idler, so that linear movement of said actuator in one direction or the other produces rotation of said sprocket likewise in one direction or the other, means for coupling said sprocket to said boom for positively imparting motion of the actuator in either direction to the boom for lowering the boom and forcibly feeding it into the ground to the digging position, and for raising the boom to an elevated position, and means including an adjustable wedge block interposed between said sprocket and said idler for producing static tension in said chain.

3. In a hydraulic operator for a trenching boom, said boom having a rotatable boom housing journalled in a main frame, the combination comprising, a subframe mounted on said main frame, said sub-frame having parallel walls and an end portion, a sprocket and an idler journalled in the walls of said sub-frame and spaced from one another in line with the end portion of said sub-frame, a loop of chain trained about said sprocket and said idler, and a double-acting hydraulic actuator mounted on the end portion of said sub-frame and having a plunger coupled to said chain at the straight run portion thereof defined by said sprocket and said idler, so that linear movement of said actuator plunger in one direction or the other produces rotation of said sprocket likewise in one direction or the other, means for coupling said sprocket to said boom housing for positively imparting motion of the plunger in either direction tothe boom housing, for lowering the trenching boom and forcibly feeding it into the ground to the digging position and for raising the boom to an elevated position, and means coupled to the side walls of the sub-frame at a point remote from said sprocket for suspendingly connecting the sub-frame to the main frame.

4. In a hydraulic operator for a trenching boom, said boom having a boom housing rotatably mounted on the frame of a movable vehicle, the combination comprising a sub-frame mounted on the frame of said vehicle, said sub-frame having side walls and an end portion, means journaling said boom housing in said sub-frame spaced from the end portion thereof, a double-acting hydraulic actuator mounted on the end portion of said sub-frame and having a plunger arranged to operate substantially in line with the end portion of said sub-frame and the rotatable boom housing, and a connection coupling said plunger and said rotatable boom housing so that linear movement of said actuator plunger in one direction or the other produces rotation of said boom housing likewise in one direction or the other, said connection providing for positively imparting motion of the plunger in alternate directions to the boom housing, for lowering the trenching boom and forcibly feeding it into the ground to the digging position and for raising the boom to an elevated position, and means coupled to the walls of the sub-frame at a point remote from said rotatable boom housing for suspendingly connecting the sub-frame to the frame of the vehicle.

References Cited in the file of this patent UNITED STATES PATENTS 286,900 Burke Oct. 16, 1883 1,955,154 Temple Apr. 17, 1934 2,330,802 Andersen et al. Oct. 5, 1943 2,519,075 Schmidt Aug. 15, 1950 2,519,076 Schmidt Aug. 15, 1950 2,519,077 Schmidt Aug. 15, 1950 2,637,259 Acton May 5, 1953 2,714,773 Stewart Aug. 9, 1955 

